This invention relates to controlled deployment of medical devices such as endoprostheses and balloons.
Prostheses are used in body lumens that have been occluded or weakened by disease. For example, to treat arterial stenoses, an endovascular stent is implanted to hold the lumen open and to prevent any flaps or dissections on the lumen wall from occluding the lumen. To treat aneurysms, a prosthesis in the form of a graft is attached to healthy portions of the lumen on either side of the aneurysm so that the body of the graft bridges the weakened area. The wall of these grafts is initially permeable, but through clotting action, becomes fluid impermeable. This reduces the pressure in the aneurysm and hence, the likelihood that it will rupture.
Prostheses are typically delivered into the body on a catheter in small diameter form and then expanded to engage the lumen at the desired site. They may be self-expanding, i.e., they expand from a small diameter to a larger diameter by their own elastic forces after removal of a restraint, or they may be expanded by radial force from within the prosthesis, provided, for example, by an inflatable balloon on the end of the catheter.
In a procedure known as valvuloplasty, a balloon is used to open a valve in the heart. In this case, the physician urges the catheter through the closed valve to position the balloon beyond it. A controlled inflation is then effected such that the distal end of the balloon inflates to a diameter larger than the valve. The catheter is then withdrawn proximally until the physician feels resistance caused by the inflated portion of the balloon engaging the inner walls of the valve. A proximal portion of the balloon is then inflated which centers the balloon about the valve. Finally, the central portion of the balloon is inflated to dilate the valve.